If there are plenty of roots left, and the crown isn't damaged, perhaps they'll survive. Knockout roses are pretty hard to kill. At least you're in the right time of the year to be doing this kind of work. Roses do well from drastic cutting back in the dormant season.

With such a damaged root system, watering will have to be carefully scheduled if you want them to live. Sprinker spray too much and you risk black spot (although Knockout is relatively fungus resistant), or crown rot. Roses REALLY like drip irrigation if that's an option.

But here's my thinking. IF the roses live, it will take a year for them to grow back to the 5 gallon size they were before. Will the customer be ok with waiting for that? And what if one or two die? Will they be ok with having roses of different sizes for a few years after you replace a couple and wait for them to grow in?

That's a much better thought out response than the first one I quoted.....thanks man I appreciate it. Makes more sense with what you wrote the second time. I agree with that a lot more. I didn't even think about if some make it and some don't the different sizes. I also wasn't considering if that would bother the client if it took another year to get back to a decent size. Some good things to think about for sure! Thanks.